kvm/riscv: rework guest entry logic

kvm/riscv: rework guest entry logic

In kvm_arch_vcpu_ioctl_run() we enter an RCU extended quiescent state
(EQS) by calling guest_enter_irqoff(), and unmask IRQs prior to exiting
the EQS by calling guest_exit(). As the IRQ entry code will not wake RCU
in this case, we may run the core IRQ code and IRQ handler without RCU
watching, leading to various potential problems.

Additionally, we do not inform lockdep or tracing that interrupts will
be enabled during guest execution, which caan lead to misleading traces
and warnings that interrupts have been enabled for overly-long periods.

This patch fixes these issues by using the new timing and context
entry/exit helpers to ensure that interrupts are handled during guest
vtime but with RCU watching, with a sequence:

	guest_timing_enter_irqoff();

	guest_state_enter_irqoff();
	< run the vcpu >
	guest_state_exit_irqoff();

	< take any pending IRQs >

	guest_timing_exit_irqoff();

Since instrumentation may make use of RCU, we must also ensure that no
instrumented code is run during the EQS. I've split out the critical
section into a new kvm_riscv_enter_exit_vcpu() helper which is marked
noinstr.

Fixes: 69c9acb307a7c93f ("RISC-V: Add initial skeletal KVM support")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Anup Patel <anup@brainfault.org>
Cc: Atish Patra <atishp@atishpatra.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Tested-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Anup Patel <anup@brainfault.org>